Mysql SQL多表查询,联接语法
我有以下建议: 表字段名称 活动的activeID,activeName 活动类别活动ID,类别ID CategoriescategoryID,categoryNameMysql SQL多表查询,联接语法,mysql,sql,syntax,Mysql,Sql,Syntax,我有以下建议: 表字段名称 活动的activeID,activeName 活动类别活动ID,类别ID CategoriescategoryID,categoryName from Active a left join (select b.activeID activeID, c.categoryName CategoryName from ActiveCategories b left join Categories c on b
from Active a
left join (select b.activeID activeID, c.categoryName CategoryName
from ActiveCategories b
left join Categories c on b.categoryID = c.categoryID) d
on a.activeID = d.activeID
我希望查询,以便结果获取ActiveCategories上活动的左连接,但它应该显示相应的categoryName[来自Categories],而不是CategoryID[来自ActiveCategories]整数。
到目前为止,我已成功显示整数,但没有显示相应的名称。请尝试:
选择a.activeID、a.activeName、d.categoryName
from Active a
left join (select b.activeID activeID, c.categoryName CategoryName
from ActiveCategories b
left join Categories c on b.categoryID = c.categoryID) d
on a.activeID = d.activeID
您可以向我们展示您尝试过的任何内容吗?您只需要添加另一个与Categories表的联接。为什么这对您不起作用?我的尝试>>>sql=SELECT Active.*,ActiveCategories.CategoryID从Active左侧加入Active上的ActiveCategories.ActiveID=ActiveCategories.ActiveID[ActiveID]您可能希望coalescc.categoryName,'Unknown'作为categoryName